Tension indicating devices for instance in roof bolting



Feb. 16, 1965 R F. TAYLOR 3,169,440

TENSION INDICATING DEVICES FOR INSTANCE IN ROOF BOLTING Filed Sept. 5. 1961 2 Sheets-Sheet 1 la /ammo [PAM/s Dr; 02

BY Jwd R. F. TAYLOR Feb. 16, 1965 TENSION INDICATING DEVICES FOR INSTANCE IN ROOF BOLTING Filed Sept. 5, 1961 2 Sheets-Sheet 2 hwavme R/cH/Mw Ammo/5 74m 0/? 5 Y rim K Wu United States Patent 3,169,440 TENdiGN INDKQATENG DEVHCES FOR ENSTANCE 1N ROSE BOLTENG Richard Francis Taylor, Eohannesburg, Transvaal, Republie of South Africa, assignor to Angie-Transvaal (3onsolidated investment Company Limited Filed Sept. 5, 1961, er. No. 136,974 Claims priority, application Republic of South Africa, Sept. 9, 1960, 3,689/60 4 Claims. (Cl. 85-62) This invention relates to tension indicating devices. Although the purpose for which it was designed is to indicate the tension in roof bolts and this specification will discuss the device in relation to roof bolting, it is to be understood that the invention has wider application.

The art of roof bolting in mining tunnelling and so on is well known and widely practised. It is equally well known that the etlicacy of the system depends upon the maintenance of the tension in the bolts in a predetermined range.

At installation, the use of a torque wrench is some assurance that the bolt sets out on its career in proper condition, although even this is not sure because of various imponderables such as variations in the screwthreading and in friction losses. However, even if the initial tension is correct, it will not necessarily remain so.

It is important from the point of view of safety and the general well-being of the mine that variations in tension outside a permitted range be detected and corrected. This involves periodic inspection of the bolts, which are usually not easily accessible and often all but invisible. These and other difiiculties have detracted from the value of known indicating devices.

The object of the present invention is to provide an indicating device which is accurate, is capable of being easily inspected at a distance and except possibly where very accurate measurements are required for research work avoids the necessity of any measurement.

According to the invention the indicating device consists in a resiliently deformable body adapted to be springily deformed by tightening of the bolt, and indicator means projecting from the body and adapted to show the extent of deformation of the body.

Further according to the invention the body is a washer and the indicating means consists in at least one formation fast with the washer at or towards its periphery and extending forwardly from the convex face of the washer.

It will be appreciated that the degree of distortion of the washer due to the tightening of the bolt is a measure of the tension in the bolt, and that as the washer is progressively distorted, the angularity of the formation to the rock surface or intervening washer is correspondingly varied.

Thus the angularity of the formation at any time is a measure of the extent of deformation and correspondingly of the tension in the bolt.

T o facilitate measurement of this angularity the invention provides a datum from which it can be readily observed. This may be a fixed datum such as a rigid projection from the bolt itself, but preferably it is another formation, diametrally opposed to the first. The angularity' of each (being equal) is indicated by the distance apart of the formations, which distance is thus a measurement of the tension in the bolt. Under certain circumstances more than one fixed datum and/or pair of formations may be provided.

The invention consists also in the combination with the body and the indicating means discussed above of a gauge that measures the angularity of the formation to ice the bolt by means of the distance between the formation and a fixed datum, or between two opposed formations.

Various embodiments of the invention are illustrated in the accompanying drawings in which:

FIGURE 1 is a side view, partly sectioned of one embodiment utilizing one type of gauge,

FIGURE 2 is a side view of a second kind of gauge,

FIGURE 3 is a side view of a third kind of gauge,

FIGURE 4 is a side View of a fourth kind of gauge,

FIGURE 5 is a view of a hand measuring gauge,

FIGURE 6 is a perspective view of the Washer use in FIGURE 1,

FIGURE 7 is a view of an alternative form of body,

FIGURE 8 is a section on the line 8-8 of FIGURE '7, and

FIGURE 9 is a view of still another alternative form of body.

In the drawings, the roof bolt 19 having a head 13 extends into a bore 12 in the rock face 14 where it is screwed into a captive nut that causes some Wedging device or other to be expanded tightly against the wall of the bore. The nut and the wedging device are not illustrated, as they may take the form of any one of a large number of known kinds. Alternatively the unthreaded end of a stud may be anchored in the hole as by grouting and the head 13 is a nut screwed on to the stud.

interposed between the head 13 of the bolt 10 and the fact 14 is a dished washer 16 having concave and convex sides and that either bears against the face, if the latter be flat, or against a Hat Washer 18 if it be not. The concavity of the washer 16 is directed away from the bolt head.

The dished washer 16 has, integral with it, two wing formations or lugs 20, 21 projecting away from the periphery of its convex face. These lugs extend away from washer 16 in substantially, parallel relationship and have opposed holes 22, 23 towards their free ends.

Between the head of the bolt it) and the washer 16 there is a spherical seat washer 19. In an appropriate case the head can bear directly on the washer 16 or a fiat or cupped washer could be used in place of the washer 153. The latter is preferred because the spherical shape tends to compensate for an irregularity if the hole for the bolt is at an angle to the roof. V

The dished washer 1a is flattened as the bolt is screwed home, and, as explained above, the extent of deformation of the washer is directly propontional to the tension in the bolt 1% As the washer is flattened, the lugs 20, 21 are caused to swing toward each other so that the extent of their deflection, and hence their distance apart, are measures of such tension.

To enable the spacing of the lugs to be visually inspected, a gauge is provided that is engaged with the lugs in a position of the lugs in which they are swung toward each other, corresponding to a tensioned condition of bolt 19. In the form shown in FIGURE 1, this gauge consists in a V-shaped metal plate 24, having shanks 26, 23. One shank 26 is notched at 30, while the other is plain.

While the bolt itlis being screwed home, the gauge is engaged in the hole 22, with the notch 30 in register with lug 2%. As the tension in the bolt increases, the washer 16 is flattened, the lugs 20, 21 converge, and the shank 28 progressively enters the hole 23. Indeed, the extent of penetration of the shank may be used as an indication of the desired tension, without the use of a torque wrench.

As the tension subsides in use, the lugs diverge until, when a predetermined minimum figure is reached, the gauge is dimensioned for the shank 28 to become disengaged from the lug 21. Thus, notch 30 and shank 28 are spaced apart a distance less than the distance between lugs 20, 21 when thewasheriis undeformed, so that bolt tension lessens and the washer returns toward its uncleformedconfiguration,.one end of the gauge will fall' down. The gauge then dangles from the lug 20, offering a plain visual signal that the .bolt needs'tightening.

Withth e washenofFlGURE 7 at lowtensions the wings 'ilfirst make contact with theflat. washer '18 (or the roof in the absence. of such'a Washer). As the ten sion increases the contact line widens to something simi- In other words, the free enfdsoflugs ztl and Eliare 1 spaced farther apart in the uncompressed condition oft hewasher than when thewasheri is compressed in use.

In FIGURE 2.the gauge is shownlas having one shank 32 with several steps 34. The particular step that is en-' gaged' at any time withgthe lug 21 is a measure of the tension'intheibolt. Thcsteps may .be-joined by'inclined ;sur faces $6, so that if the tension rises, as sometimes occurs," the gauge can f HlQVB upwardly. The distance be tween lugsZthZl, and the distances between the notch that corresponds 'tovnotch 36 and the steps, are so related that asthelbolt tension decreases and the washer gradually resumes its undeformed condition, the h1g2}.

,jWlll rnove lengthwise outwardly from step to step of the shank 32, thereby to give azsornewhatquantitative'indica 'tion of the'bolt tension Finally, one end of the gauge fallsdown as before. V

- In'FIGURE 3 the gauge .isfshownwith shanks 38,40

'inthe same direction. This gauge is designed toiindicate a dangerous rise in tension. i I i 1 7 l In FIGURE 4, the gauge isin several parts 42, 43, 44 side by'side', eaeh dimensioned to become disengaged at a different tension; Thus, as the bolt-slackens, one part after 'anothe drops away. {The parts maybe differently very' rapid and sure inspection.

Alternativelyv the formations r'nayfbe comprised in an electricalcircuit and theresistance between them used as anindication of the tension.

, In FIGURE a hand measuring gauge is illustrated. The gauge has notchesSl corresponding'tq different values of tension. It maybe calibratedas shown. -By inserting the gauge between two lugs and 21 the bolt tension at any given instant may bemeasured.

' 22, 23 and making the device inaccurate.

lar to that shown in FIGURE 1.

Note also that-the Wider the contact line, the higher the hysteresis of the Washer becomes,

I v Awasher till with extremely low hysteresis is illustrated in'FiGURE 9. .In' this case the washer is in effect a leaf spring tliat'has been holed at 31 to be threaded over the bolt and that is'slightly widened around the hole 81 and bent for purposes ofstrength. In this case the contact between the washer 89 and a flat Washer such as itsin FIGURE 1 progressively widens as the tension increases;

The accuracy of measurement at'low tensions remains the highestbut accuracy at higher tensions is not substantially impaired.

It may be necessaryto use a plastic 'insert in one or both of'the lug holes in orderto ensure that rusting does not take place, thereby impairing the edges of theholes I Furthermore, the distancebetween'the edges'on each lug hole can'b more accurately controlled in manufacture.

' diametrically opposed iwing formations extending from 3 Manyotherforms of i dicator are possible. It'is'notr sion in the bolt is utiliza ble; that any of the forms can be allied with warning devices of r'nanyjkinds, such as warn- Furtherrnore, the device of the invention canbe developed by mechanical or othenmearis to multiplyxthe dis'placement of the formations to. promotejaccuracy' of 1 ;reading or of observation. *addititinalspringy bodies operatinginconjunction with thernain body, with; or without additional displaceable formations. i a I 'Thetwasher 16 may be round but is preferably .ellipsoidal, as shown. Where it is desired toincrease "the For instance there may be amount; of movement at low tensions compared with the .a'rnount of movementat'high tensions, :the lugs are ex- .tended from the body of the wash'er as shown. in FIGURE 7 so that the washer has wings '71 extending fromit and from-whichthe lugsztl and ZLdepend.

thought necessary to enumerate them all. 'Suflice it to say'that any means which will'rneasure'the extent of dis placement of the formationor formations due to the tening lights; bells and :so on; and'that the behaviourjof'the boltcan be recordedif desired. 7

The disadvantage'of using plastic insertsis, of course, increased manufacturing costs Iclairn: 1

. l. The combination of an anchorjbolt having ahead,

a stern andanchoring means; a continuous tension indicatingdevice consisting in a resiliently deformable washer having co'ncaveand convex sides. adapted to be springily deformed byithe'head on tightening of the bolt and having a central opening to receive the bolt shank; two

theperiphery of the convex side and having opposed holes ineaeh formation; a gauge spanning the distance between I the two formations'and'having endlshanksthat enter the holes inthe formations; and a notch. on one end shank for hangingthe g'ange from one of said formations; the others shank being istr'aight,

3. The. device .of claim '1 in which said notch andsaid straight shankare' spaced apart a distance less than the distancabetween said formations when the washer is.un-

deformed, so that said straight'shank become disengaged fand drops from its formation when the spacing apart of the formations, and therefore the bolt tension, diverges from a predetermined value. v '4. Thedevice of claim 1 in which the gauge has one end =shank that is held by'on'e formation, and a second "end shank that is. stepped' and supported by'the other forrnatiomlthe distancebetween said formations andthe distances between said one end shank and the steps of the stepped end shan ksbeing.suchthat the steps of the stepped end shank progressively becomedisengaged and drop 'fromthe formation supporting thestepped shank, as the spacing apart of. the formations diverges froma predeter, .rnined value in respect of each step. I a

. .References Cited by the Enaminer;

-1UNlTED STATES PATENTS.

' 1,774,695 9/30 Baynes 6i EDWARD C ALLEN,Primtzry Examiner. a

QARLSV. 'roMLr Examiner.

2. The combination claimed inclaim linrwliich said otherrend shank ishooked to extend .in the samedirection as the firstend shank. i 

1. THE COMBINATION OF AN ANCHOR BOLTS HAVING A HEAD, A STEM AND ANCHORING MEANS; A CONTINUOUS TENSION INDICATING DEVICE CONSISTING IN A RESILIENTLY DEFORMABLE WASHER HAVING CONCAVE AND CONVEX SIDES ADAPTED TO BE SPRINGILY DEFORMED BY THE HEAD ON TIGHTENING OF THE BOLT AND HAVING A CENTRAL OPENING TO RECEIVE THE BOLT SHANK; TWO DIAMETRICALLY OPPOSED WING FORMATIONS EXTENDING FROM 